Investigation of micro-adhesion by atomic force microscopy

Abstract

Atomic force microscopy (AFM) was used to investigate the micro-adhesive interactions between solid interfaces. By operating the force calibration mode of AFM at different ambient (in air, in water and charge eliminated in air), the main factors of micro-adhesion (van der Waals force, capillary force and electrostatic force) of a sample were separated, measured and compared in a single measurement for lamellar materials, such as graphite, MoS 2 and mica. It is found that on an average, the capillary force, which is determined by environmental humidity, has the largest contribution to the adhesive interactions at the present conditions of 50% humidity. The van der Waals, which is defined by material properties, has the smallest impact for graphite. For dielectric materials, the electrostatic effect is a little weaker than capillary force, but much stronger than van der Waals effect. The results infer that at micro-dimensions or nano-dimensions, it is the environmental conditions, not the material properties that play the most important role on adhesive interactions between solids.